The following has been typical as a conventional photoconductive antenna. That is one in which each of a pair of electrodes formed on a semiconductor layer is constituted by an antenna part forming an antenna region for generating or detecting a terahertz electromagnetic wave, a pad part connectable to an external lead, and a line part connecting the antenna and pad parts to each other. Here, the line part is formed linear (see, for example, Patent Document 1). The line part in a pair of electrodes is thus formed linear, since characteristics of the photoconductive antenna element will deteriorate unless the line part has a predetermined linear length.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-207288